A canister type vacuum cleaner is illustrated in the patents incorporated by reference herein and includes a reduced velocity chamber with a high velocity air inlet. Air is drawn into the chamber by an electric motor which drives a rotary means, or fan, for creating vacuum in the chamber to draw air laden with particulate material through the chamber and force it from the outlet as exhausted clean air. Canister type vacuum cleaners normally include a conical filter extending downwardly into the canister or low velocity chamber and formed of a porous mat to remove the dirt and debris carried by the air coming into the canister. The high velocity air drawn into the chamber has a tendency to entrain large solid particles which are brought into the low velocity chamber where the air is then swirled or vortexed in a centrifuge configuration with convolutions so that large particles carried into the chamber with the inlet air are extracted by the vortexed or cyclonic action of the air in the canister. Thereafter, the air is pulled upwardly through the conical filter mat or porous layer toward an upper motor that drives a fan for creating a vacuum in the canister, or reduced velocity chamber, so that the air flowing upwardly through the conical filter passes through a filter disc and outwardly through an exhaust passage, or passages, above the canister. Stevenson U.S. Pat. No. 5,248,323 developed an improvement to filters for vacuum cleaners by developing an activated charcoal containing filter which efficiently remove gaseous impurities, such as paint fumes and other odor creating gases which are in the air and pass through the vacuum cleaner.
The canister type vacuum cleaner, as so far described, only removes the relatively large particles entrained in the air. Air particles of a size less than 10 microns pass freely through the filter medium and are recirculated in the room. Many of these small particles can act as irritants to an individual and the recirculation of such particles can increase the irritation to an individual. High density filters must be employed to filter out very small particles in the air; however, high density filters cause large pressure drops through the filter thus cannot be used in standard vacuum cleaners or other air filtering systems.
In summary, vacuum cleaners, in general, canister type vacuum cleaners, in specific, have not been able to remove very small particles entrained in the air.